The present invention relates generally to a novel suspension system for the rotor component in a rotor/stator assembly, and more particularly to such a system which provides for passive and stable suspension of the rotor. Assemblies utilizing the features of the present invention are adapted for a wide variety of applications, including fluid handling systems for fragile or aggressive fluids, as well as for other applications pertaining to instrumentation, as well as applications for such assemblies which may be characterized as either delicate and/or rugged. The novel passive and stable suspension system of the present invention includes a rotor which is typically suspended within a stator, with the rotor being stabilized through passive magnetic as well as hydrodynamic forces.
The magnetic components may be designed in a variety of different coupling arrangements, with passive magnetic bearings being employed for creating stability along certain selected planes or axes and further creating one resultant unstable negative force in one plane or along an axis. More specifically, the magnetic forces are designed to create an unstable negative force in a plane perpendicular to the axis of rotation of the rotor, with stable and positive forces and moments being created in all other degrees of freedom excepting of course, rotation of the rotor. This resultant instability in the axis of rotation is overcome upon rotation of the rotor creating a centrifugal force of magnitude greater than that of the unstable negative force. In other words, when rotating, the forces created in the rotor return the body to an appropriate point of origin for the intersection of the X, Y and Z axes.
The suspension system of the present invention utilizes magnetic bearings for creation of positive stiffness and a resultant negative stiffness, with the overall stiffness in five of the six degrees of freedom being positive. Dynamic stability of the system is ultimately achieved through centrifugal/centripital forces, with dynamic stability being achieved.
Except for the passive magnetic stabilization system and the dynamic magnetic forces utilized to drive the rotor, assemblies of the present invention are otherwise bearing and seal-free. Passive magnetic forces are applied to the rotor during periods of rotation and dwell, with these passive forces including a resultant unstable negative force in a plane or along an axis perpendicular to the axis of rotation. As such, assemblies employing the magnetically stabilized rotor/stator assemblies of the present invention are particularly well adapted for a wide variety of mechanical applications, with one such application being in a centrifugal pump for handling highly aggressive such as corrosive, poisonous, or dangerously radioactive fluids, as well as fragile fluids including human or animal blood. During any transfer/movement of such fluids, it is frequently dangerous to expose the structure to forces such as unusual impact and/or shear forces, and thus the advantage of utilizing bearing and seal-free pumps, and particularly one wherein the rotor/stator assembly is at least partially magnetically stabilized. A particular advantageous feature of the present invention is that of providing a passive magnetic force to the rotor which when combined with the centrifugal forces, reduces and/or completely eliminates surface-to-surface contact between rotor and stator surfaces.
In connection with one application of the present invention, pump assemblies utilizing the features of the present invention may be exposed to aggressive fluids, including corrosion, poisonous or radioactive fluids, as well as fluids which cannot tolerate contamination. Through elimination of seals and/or bearings the lifetime and/or longevity of the pump or other assembly or structure is increased.
Poisonous fluids, for example, become extremely dangerous whenever leakage develops, a common consequence of bearing failure. In pump applications for the present invention, a rotor or impeller is utilized in an assembly which is bearing and seal-free, with the rotor being dynamically balanced and stable during operation. Bearing and seal-free pumps utilizing the rotor/stator assemblies of the present invention are particularly well adapted for transferring human blood and other delicate liquids without damaging and/or otherwise significantly adversely affecting their composition or quality. Furthermore, the magnetic stabilization feature of the present invention provides stable positioning of the rotor during operation. Depending upon the application, the rotor may be fabricated from any of a variety of non-magnetic materials, including, for example, metals such as titanium and non-metals such as pyrolytic carbon. Certain engineered plastics have also been found useful.
Another feature of rotors and stators suitable for application in the present invention is that they be capable of receiving and reliably retaining passive magnetic components which deliver forces stabilizing the rotor. Although not in the form of a mechanical surface-contacting bearing, the passive magnetic components utilized in the present invention may be positioned and/or arranged to function as magnetic thrust bearings. The rotor is also arranged to be capable of receiving and reliably retaining magnetic components such as electromagnetic components used in the drive system for delivering energy to the rotor for rotation. Generally, an array of permanent magnets are positioned within the rotor and stator components in a brushless motor configuration. Alternatively, the drive mechanism may employ permanent magnet-to-permanent magnet couplings similarly mounted. The arrangement of the present invention provides for the economic utilization of a magnetically levitated rotor/stator assembly which may be fabricated by conventional processes, and therefore highly economically viable. Rotor stabilization and/or suspension may be achieved with passive magnetic bearings such as positioned in different arrangements or configurations. In preferred configurations, magnetically coupled bearings may provide positive forces in five of the six possible degrees of freedom, while providing one unstable negative force, preferably in a plane perpendicular to the axis of rotation, with this instability being overcome by a centrifugal force of greater magnitude.